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Clean Cooling Towers: The Overlooked Key to Water and Electricity Savings

Many people consider cooling tower cleaning to be an additional expense. However, the correct perspective is: maintaining a clean cooling tower is an investment that yields real financial returns. A clean cooling tower is not just about avoiding damage, but about achieving peak operational efficiency that saves two of the most valuable resources: WATER and ELECTRICITY.

So, how does a clean cooling tower work to create savings? Let's discuss this in detail.

Part 1: How Clean Cooling Towers Save WATER

Cooling towers cool water through evaporation. Every time water evaporates, heat is released into the air, and the remaining water becomes cooler. However, this process comes at the ‘cost’ of water loss.

1. Reducing Low Forced Concentration Cycles (COC)

  • What is COC? COC is the ratio of dissolved minerals in circulating water to minerals in make-up water (replacement raw water). A high COC means that we reuse water many times before disposing of it.

  • Relationship with Contamination: When cooling towers are contaminated with sludge, algae, and scale, minerals in the water are more likely to precipitate and exacerbate the condition. To prevent scale formation that can clog the system, operators are often forced to discharge more water (blowdown) at a high frequency. This means that the COC becomes low.

  • When the Cooling Tower is Clean: Clean surfaces minimise nucleation points for scale formation. With the same water conditions, we can safely increase the COC. With a higher COC:

    • The same amount of water is evaporated, but MUCH LESS water is discharged (blowdown).

    • Illustration: Increasing the COC from 3 to 5 can reduce blowdown water consumption by approximately 15%.

Water Saving Mechanism #1: A clean cooling tower allows operation at a higher COC, which directly reduces the volume of blowdown and make-up water.

2. Minimising Other Water Loss

  • Drift (Wind-borne Droplets): Clean fill pack and drift eliminators function optimally. Mud-clogged drift eliminators cannot capture water droplets properly, causing more water to be wasted through drift.

  • Hidden Leaks: Routine cleaning is a good time to check for leaks in basins, pipes, or joints that have not been visible.

Part 2: How Clean Cooling Towers Save ELECTRICITY

Electricity savings occur in the two main pieces of equipment that consume the most energy in a cooling tower system: PUMPS and FANS.

1. Reducing the Workload of the Circulation PUMP

  • Flow Resistance (Pressure Drop): Clean fillers have wide open gaps for water and air flow. Conversely, fillers that are dirty and clogged with moss, scale, and mud become like clogged filters. Water has difficulty flowing, causing a significant increase in pressure drop.

  • Pump Law: To counteract high pressure drop, the pump must work harder and draw more electrical power to maintain the same flow rate.

  • When the Cooling Tower is Clean: Pressure drop across the fill pack and nozzle is minimal. The pump can circulate water easily, using less electrical power to perform the same task.

Electricity Saving Mechanism #1: Clean fillers reduce system pressure drop, ease the workload on the pump, and reduce its electricity consumption.

2. Reducing the Workload on FANS

  • Optimal Heat Transfer: The main task of the filler is to maximise the contact surface area between water and air. A clean filler ensures that the water spreads evenly as a thin film, allowing for highly efficient heat transfer and evaporation.

  • Hindered Heat Transfer: Biofilm and scale deposits on the fill pack act as heat insulators. These deposits prevent heat from transferring from the water to the air. As a result, the outlet water temperature cannot reach the desired target.

  • Fans Forced to ‘Overwork’: To compensate for this poor heat transfer efficiency, the control system will instruct the fans to spin faster, drawing in more air. Fans spinning faster require exponentially more electrical power (Fan Affinity Law: Power ≈ (RPM)³).

Electricity Saving Mechanism #2: Clean fillers restore heat transfer efficiency, allowing the fan to operate at a lower speed (or for a shorter operating time) to achieve the same cooling results, which drastically saves electricity.

Conclusion

Investing time and money in a planned cooling tower cleaning and maintenance programme is not an expense, but rather an operational efficiency strategy. A clean cooling tower creates a positive domino effect:

  1. Saves Water by minimising blowdown and drift.

  2. Saving Electricity by reducing the workload on pumps and fans.

In the long term, these water and electricity cost savings will far exceed the maintenance costs themselves, while extending equipment life and preventing costly downtime.